FIG. 1 is a structural diagram of a magnetic multi-layer thin film 1 forming a GMR-type or TMR-type angle sensor, including an anti-ferromagnetic layer 2, a ferromagnetic reference layer 3, a nonmagnetic spacer layer 4 and a ferromagnetic free layer 5. Resistance between two ends of the magnetic multi-layer thin film is under the control of a relative angle between the ferromagnetic free layer 5 and the ferromagnetic reference layer 3. In actual operation, as shown in FIG. 2, a rotary permanent magnet 6 generates a rotational magnetic field 8 on the surface of a packaged GMR-type or TMR-type angle sensor chip 7. The rotational magnetic field 8 is required to be greater than the saturation magnetic field value of the ferromagnetic free layer 5 and smaller than the pinning field value of the ferromagnetic reference layer 3. In this case, the magnetization direction of the ferromagnetic free layer 5 is the same as the direction of the rotational magnetic field 8. The angle of the rotational magnetic field is measured by measuring a change in the resistance between two ends of the magnetic multi-layer thin film 1 as the angle of the rotational magnetic field changes. FIG. 3 shows a biaxial angle sensor, i.e., the sensor includes a multi-layer thin film structure with a ferromagnetic reference layer along the X-axis direction and a multi-layer thin film structure with a ferromagnetic reference layer along the Y-axis direction, and output signals of the structures at two ends are a sine signal 9 and a cosine signal 10. An angle signal value of the biaxial angle sensor is obtained by means of arctangent calculation on the output signals thereof.
However, actually, the amplitude of the rotational external magnetic field of an angle sensor designed by using the foregoing GMR-type or TMR-type magnetic multi-layer thin film structure should be less than 300 G, and a rotational external magnetic field with higher amplitude may cause the ferromagnetic reference layer 3 to rotate, thus generating a non-linear output. FIG. 4 shows an ideal angle signal curve 11. When the rotational magnetic field is 50 Oe, an output curve 12 thereof is close to the ideal sine-cosine curve 11, and when the rotational external magnetic field exceeds 400 Oe, an output curve 13 thereof deviates from the ideal curve 11 and becomes triangular, thus generating an angle error curve 14.
However, many applications require the amplitude of the working rotational external magnetic field to be greater than 300 G, and also require a low non-linear error. Therefore, it is urgent to develop a novel angle sensor that can operate in the presence of a high intensity rotational magnetic field while generating low non-linearity error.